This invention relates generally to memory-programmable controls for the process cycles of processing machines using multiprocessor systems, and more particularly to a memory-programmable control having processor units, coupling memories and input and output modules, each processor unit having a subprogram and a data memory of its own.
Multiprocessor systems of the type having processor units for coupling memories and input and output modules for signals which are conducted via a common bus, and which have respective subprograms and data memories which can be accessed independently of the common bus, are known to operate in conjunction with a bus control which releases access to the common bus for only one of the processor units at a time. Such multiprocessor systems find application in regulation and control engineering. A detailed description of such systems can be found, for example, in the journal "Elektronik", 1982, pages 76 to 95. If the individual processors have a common bus, the problem of bus assignment always arises. In the known methods, either a processor having the highest priority is given access to the bus, or a processor transfers, after its program has been executed, the common bus to the next bus processor. All such bus assignment systems are relatively uncritical as long as real process on a processing machine does not have to be controlled directly. In such a case, particularly if very fast processes are involved, the correct assignment and synchronization of the individual processors with each other and to the process are relatively elaborate and complicated. Moreover, it is quite difficult to guarantee defined reaction times with respect to certain events in the process.
Freely programmable controls which utilize microprocessors are well known and are utilized for controlling processing machines. In such controls, the output signals which are required for the process are made available from the measured input signals in accordance with a cyclically executed program. Such controls are described, for example, in Siemens-Zeitschrift "Energietechnik" 1982, no. 2, pages 54 to 57, or Siemens "Energietechnik" 1979, pages 136 to 139, Siemens-Zeitschrift 1979, pages 43 to 47, European Patent Application No. 10 170, DE-AS No. 25 00 320, and U.S. Pat. Nos. 3,921,146 or 3,942,158.
Some of these known programmable controls do not operate directly with the input and output signals, but rather with a so-called process image. In such systems, the programmable oontrols operate at the beginning of each processing cycle, at which time the input signals are interrogated and recorded in a data memory. The user program then operates with the stored data and generates the output signals therefrom. The stored output signals are issued at the end of the processing cycle to the associated output modules for the process. A control of this type is described, for example, in the above-mentioned European Application No. 10 170.
It is, therefore, an object of this invention to provide a simple freely programmable control for use in multiprocessor technology with which simple synchronization of the individual processor units with each other and with respect to bus access is possible, and with which defined reaction times can be guaranteed.